Physiology of the Airway Flashcards
What is the role of the hard palate?
It divides the nasal and oral cavities
Where is the hypopharynx?
The lower part of the pharynx below the nasal and oral cavities, but before the larynx
What feature of the airway is unique to humans?
It is at a right-angle
Whether breathing is through the nose or mouth, it must turn a corner to enter the airways
Why does the hard palate appear white on an MRI scan?
it is made of bone
What does not show up well on an MRI scan?
soft tissue such as skin and fat
What is the genioglossus?
a fan-shaped extrinsic tongue muscle
it forms the majority of the body of the tongue
What is the tensor palatini?
a broad, ribbon-like muscle which tenses the soft palate
During nasal breathing, why can’t air pass through the mouth?
The lips are closed
The tongue is in contact with both the hard palate and the soft palate
there is no pathway through the mouth
Where does air pass during nasal breathing?
through the nasal cavity, nasopharynx, past the soft palate and into the hypopharynx and through to the airway
How does the soft palate change position during mouth breathing?
the lips are open and the tongue is contracted away from the soft palate
the soft palate is relaxed and has moved backwards towards the pharynx
What is the effect of gravity on the structures of the body?
Gravity means that all the structures in the body have weight
Why does the tongue muscle have tonic activity?
It is always contracting to keep the airway open when lying down
the tongue must be lifted forwards off the back of the pharynx to keep the airway open
What type of activity is possessed by all the muscles in the airway?
they have tonic and phasic activity
Why do the muscles in the airway have phasic activity?
This is muscle contraction that occurs with the phases of breathing
all the muscles contract more during inspiration to increase the diameter of the airway and relax a bit more during expiration
why does the soft palate have tonic activity?
It is contracting all of the time to control airway activity
What is the pharyngeal dilator reflex?
a neuronal reflex in the airway
What are the components of the pharyngeal dilator reflex?
pressure receptors
trigeminal nerve
brainstem
vagus nerve
pharyngeal muscles
what is the role of the pressure receptors in the mucosa of the pharynx?
they are sensitive to the air pressure above them
if the air pressure changes, they send signals of varying rates along the trigeminal nerve
What is the role of the brainstem in the pharyngeal dilator reflex?
it processes information received from the trigeminal nerve
it then sends an impulse down the vagus nerve to the pharyngeal muscles
this causes the pharyngeal muscles to contract or relax
What happens when the pharyngeal muscles contract or relax?
It changes the pressure in the airways
What is the action of the pharyngeal muscles when there is a low pressure in the airway and why?
When the pressure is low, there is increased effort by the lungs to move air through the airway
Pharyngeal muscles contract more to open the airway up
How long does the pharyngeal dilator reflex take and when does it occur?
50 ms
it is occurring all the time as the pressure of the pharynx is constantly monitored and the diameter of the airway changed accordingly
What reduces the efficiency of the pharyngeal dilator reflex?
drugs that slow the brainstem down
includes alcohol, sedative drugs and general anaesthetic
Why is the pharyngeal dilator reflex less efficient at night?
During sleep the brainstem becomes slower
What is sleep disordered breathing?
the change in the way the movement through the airway changes during sleep
What % of people snore and suffer from sleep apnoea?
25% of people snore
10% of people have sleep apnoea
What happens to breathing in sleep apnoea?
Patients will stop breathing for periods of 10 seconds during sleep
This misses around 2 or 3 breaths
What is the most common cause of ceased breathing in sleep apnoea?
closure of the airway
there is a very narrow gap between the soft palate and the pharynx
if the muscles relax slightly then the airway is completely blocked off
In which types of patients is sleep apnoea more common?
obese patients and after consumption of alcohol
What factor in obese patients can determine whether they have sleep apnoea?
the circumference of the neck
the compression of fat in the neck means the muscles have to work harder to keep the airways open
Which components are measured on a polysomnograph?
tidal volume
movement of the ribcage
movement of the abdomen
pharyngeal pressure
What does the tidal volume trace look like on a polysomnograph for a sleep apnoea patient?
regular breaths of around 500ml begin to fade and eventually stop
breaths stop for around 15 seconds (one apnoea)
there is a large breath as the patient recovers
How does the movement of the ribcage and the diaphragm change after obstruction in sleep apnoea?
the ribcage and the abdomen move in sync with each other during normal breathing
after obstruction, they begin to oppose each other
the ribcage muscles contract but the diaphragm can’t, due to the airway being blocked
why is the movement of the abdomen measured on a polysomnograph?
it shows the extent to which the diaphragm is working
What happens to pharyngeal pressure in a sleep apnoea patient?
with each breath after obstruction, pharyngeal pressure decreases
pharyngeal receptors fire more and more to try and make the brain do something about this
Why do patients with sleep apnoea not die?
When they stop breathing, they almost wake up
Something brings them back to a lighter level of sleep where the brain can gain control of the airway
What causes the arousal from deep sleep in sleep apnoea patients?
It is thought to be the pharyngeal receptors sending increasingly intense impulses to the brain
It may be due to oxygen levels starting to fall or carbon dioxide levels starting to rise
How is sleep apnoea quantified and what is “normal”?
quantified by the number of times the process occurs within one hour
“normal” is up to 5 times per hour
What are the symptoms of sleep apnoea?
snoring and daytime somnolence
Why do sleep apnoea patients experience daytime somnolence?
They never get any deep sleep so feel very tired in the morning
every time they wake up, adrenaline is released
this causes a small amount of sympathetic activity
What are the treatments for sleep apnoea?
- weight loss
2. CPAP machine
What is the CPAP machine?
What is the problem with this treatment method?
It applies positive pressure to the nose that forces the soft palate forwards during the night to prevent obstruction
the compliance rate is very low
Where is airway lining fluid produced?
ciliated epithelial cells and goblet cells
What are the conducting passages of the respiratory system lined with?
mucosa
a tissue which produces mucous
What do the ciliated epithelial cells look like in the nose and pharynx?
pseudostratified
this is a single layer of cells that appears as multiple layers
the cells are tall so you cannot see the junctions between them, only the nuclei
What do the ciliated epithelial cells look like in the trachea and bronchi?
they become wider columnar cells
What do the ciliated epithelial cells look like in the bronchioles?
the cells are cuboidal
How do the cells change in appearance as you go down the airway?
cells are ciliated all the way down to the bronchioles
they become progressively shorter
What is the diameter of the bronchioles?
they are passages that are less than 1 mm in diameter
What do goblet cells produce and why?
They produce mucin
They produce mucin in response to anything that irritates the airway
What are the 2 layers of fluid in the airway?
the periciliary layer
the mucous layer (gel-layer)
What is the periciliary layer?
It is saline
It is water with some salt solution within it and has low viscosity
What is the purpose of the mucous layer?
It is jelly-like in consistency and will trap any particles that are inspired
What is the purpose of the periciliary layer?
It allows the mucous layer to be moved towards the top of the lung
It will be coughed out by expiration or swallowed
How do cilia within the periciliary layer move?
They move sideways, backwards and then flick forwards
As they flick forwards they touch the underneath of the mucous layer and can move it along
At what rate does the mucous move along the airway?
How often do the cilia beat?
it moves along by 4mm per minute
the cilia beat 12 - 15 times per second
how does tobacco smoke affect the cilia?
It contains hydrogen cyanide which poisons the cilia and stops them from working effectively
This leads to a smoker’s cough
Why is a smoker’s cough worse in the morning?
During the night the cilia recover and bring all the previous day’s mucous up to the top of the lung
Other than tobacco smoke, what else can affect the cilia?
Anaesthetics stop the cilia from working, causing chest infections to occur soon after
Pollution and infections can affect the cilia
What are the functions of the airway lining fluid?
Humidification and warmth (conditioning)
Airway defence
Why does air need to be humidified and warmed by the time it reaches the alveoli?
The air must be 37 degrees and humid
The cells of the alveoli are very thin and delicate
If the air is not conditioned, the alveoli will dry out and the cells will become damaged
Why is nasal breathing better for humidification than mouth breathing?
As air goes through the nasal cavity, the meatuses mix the air up and increase the efficiency of evaporation from the lining fluid
There is also more distance to travel
How does the airway act as a “Heat and Moisture Exchanger”?
- air enters the nose and water evaporates from the airway lining fluid in the nose and pharynx
- the mucosa in the pharynx is cooled and dry
- during expiration, the air that passes through the airways is 37 degrees
the water will condense on the cooler mucosa as it leaves the body
- the same water and heat are reused during the process
How does the lung adapt to cope with different amounts of humidity in the air?
it changes the thickness of the mucous layer
What happens to the mucous layer in high humidity?
Water is absorbed by the mucous layer which swells up and holds the water
How is the constancy of the mucous layer maintained as humidity changes?
Epithelial cells detect when the movement of the cilia is impeded or becomes too free
the physical movement of the cilia causes the epithelial cells to secrete Cl- through a chloride ion channel into the pericilliary layer
Na+ follows by passive diffusion, followed by water
This changes the thickness of the layer
How does the airway lining fluid contribute to airway defence?
- expectoration
2. the muco-ciliary escalator moves particles back towards the top of the lungs and out of the body
What is cystic fibrosis caused by?
a genetic abnormality of the cystic fibrosis transmembrane regulator gene
This codes for the CFTR protein
What is the CFTR protein?
a chloride channel present on epithelial cells
What is the affect of cystic fibrosis on the airway lining fluid?
it affects the regulation of chloride in the airway lining fluid
this causes the mucous to become too viscous
What is the side effect of mucous becoming too viscous?
CF patients cannot fight off infection as pathogenic particles cannot be moved
What other factor makes cystic fibrosis patients more prone to infection?
Defensins are natural antibiotics in the airway lining fluid
In CF patients, the defensins do not work properly
this makes them more prone to infection
What is the most common presenting factor of cystic fibrosis?
a chest infection of a small baby under the age of 1
What is the smallest particle that can be seen by the naked eye?
Particles that are bigger than 5 micrometres can be seen
Particles under 5 microns can only be seen if there are many of them together - this is smoke
What is the size of a very large particle and where are they deposited?
> 8 micrometres
deposited in the nose and pharynx
What is the size of a large particle and where are they deposited?
3 - 8 micrometres
deposited in the large airways
By which mechanism do large and very large particles enter the airway?
Inertial impaction
What is inertial impaction?
particles will hit the back of the pharynx by inertial impaction
the particle has inertion which keeps it moving in a straight line when it tries to turn a corner
benefit of having a right-angled respiratory tract
What size is a small particle and where are they deposited?
0.5 - 3 micrometres
deposited in the bronchioles
By which mechanism are small particles prevented from entering the airway?
sedimentation
the weight of the particles causes them to drop out of the air onto the wall of the bronchioles
mucous in the bronchioles expels them out of the body
What size is a very small particle and where are they deposited?
<0.5 micrometres
they are not deposited, they are exhaled again by diffusion
What are examples of very large, large, small and very small particles?
very large - pollen, sawdust
large - fungal spores
small - particulate pollution, stone dust, asbestos
very small - smoke (incl. cigarettes)
How does gravity affect the number of particles in the air?
Gravity pulls most of the dust in the air down to the floor so there are very few particles in the air
without gravity, all of the particles that are formed would stay in the air forever
What is the benefit of having no gravity?
sedimentation does not occur as the particles have no weight
this is beneficial as it means more particles are expired
In inhaled drug delivery, by how much do the particles in the spray vary in size?
particles vary in size from 1 - 35 micrometers
In inhaled drug delivery, what is a large particle and where are they deposited?
What is the problem with this?
> 5 micrometers
they are deposited on the pharynx or in the large airways
they do not reach the bronchioles so are ineffective at treating most conditions
What is the side effects of inhalers containing large particles?
they are deposited on the pharynx which leads to side effects
using a steroid inhaler leads to a sore throat and infections due to the steroid on the pharynx
In inhaled drug delivery, what is a medium particle and where are they deposited?
1 - 3 microns
they are deposited in the small airways
In inhaled drug delivery, what is a small particle and where are they deposited?
0.5 - 1 microns
they are deposited in the alveolus
What are the potential uses of large, medium and small particles in inhaled drug delivery?
large - hayfever
medium - copd, asthma
small - absorption into the blood
What are the 3 non-immunological pulmonary defences?
What is significant about them?
- physical barrier and removal removes 99.9% of inhaled pathogens
- chemical inactivation
- alveolar macrophages
all of these defences are non-specific
what is the role of lysozyme within the mucous layer?
it is an enzyme that lyses cells by breaking down their cell walls
what is the role of protease enzymes within the mucous layer?
they break down proteins
e.g. elastase
what is the role of anti-protease and where is it found?
protease enzymes will also break down proteins found in our cells
anti-protease is found on the surface of epithelial cells
it prevents protease from damaging the cell if it gets too close
what is an example of an antimicrobial peptide within the mucous layer?
human beta defensins
what is the role of alveolar macrophages?
they leave the blood and come onto the surface of the alveolus
they ingest any particles they find, including pollutants and pathogens
they are the last line of non-specific defence
What is the difference between humoral and cell-mediated immunity?
humoral immunity involves chemicals
cell-mediated immunity involves cells
What components are involved in humoral immunity in the airway and where are they found?
IgA - nose and large airways
IgG - small airways
IgE - allergic disease
How are cilia involved in immunological defence?
Cilia on the epithelial cells can recognise bacteria
What happens once the bacteria is detected?
cytokines are released and an inflammatory cascade is initiated
the inflammatory response leads to a chest infection and potentially pneumonia
What are the components of cell-mediated immunity in the respiratory tract?
epithelial cells
macrophages
neutrophils in infection
eosinophils in allergy
What is the effect of carbon monoxide on the airway?
decreased oxygen carriage
what is the effect of nitrogen oxides on the airway?
airway irritation and asthma
what is the effect of ozone on the airway?
airway irritation and cough
what is the effect of particulate matter on the airway?
lung and systemic inflammatory response
what diseases is air pollution associated with a risk of?
asthma pneumonia stroke heart attack type 2 diabetes
